Carbonate and evaporite precipitates of the Abu Dhabi coastal sabkha as modern analogues to the Upper Jurassic Arab Formation (UAE)

While it is generally accepted that the coastal sabkha of Abu Dhabi represents a modern analogue to the deposits of the Upper Jurassic Arab Formation, a direct link between both systems in regards to depositional and... [ view full abstract ]

While it is generally accepted that the coastal sabkha of Abu Dhabi represents a modern analogue to the deposits of the Upper Jurassic Arab Formation, a direct link between both systems in regards to depositional and diagenetic features has never been established. Hence, initial results will be here presented that link sedimentary features observed in the Arab Formation’s ABC zones to modern microbial mat communities and evaporite deposits of the Abu Dhabi coastal sabkha. Detailed stratigraphic, core and petrographic descriptions of both the modern and the ancient will be examined and critically compared as analogues. Focus will be on those very specific characteristics that aid in the identification of similar depositional environments or specific zones, both primary and diagenetic, within those environments and, hence, facilitate the establishment of a direct link.

Our results indicate that vertical and lateral successions of lithologies in the modern and ancient show similar trends and patterns, with hardgrounds forming the base of each cycle/parasequence. A Recent hardground is usually overlain by either primary microbial or carbonate facies, or a mixture between these facies and secondary gypsum/anhydrite precipitates. Siliciclastic and halite facies occur only in the modern environment while the ancient Arab Formation is void of these sediments and precipitates. At the micro scale, modern microbial mat successions feature laminations (µm to mm scale) with embedded, possibly wind-blown, quartz grains, and vertically-displaced lithoclasts (mm to cm scale) as common primary sedimentary features. Secondary features of diagenetic origin are primarily represented by individual gypsum crystals (mm to cm scale) and anhydrite bands and nodules.

Linking the modern coastal sabkha of Abu Dhabi to the ancient sabkha of the Arab Formation is a double-edged sword: Both depositional systems appear similar as a result of comparing vertical and lateral lithologic successions while focussing on primary and early diagenetic lithologies. However, small but important differences such as the lack of clastic lithologies in the Arab Formation, point to slightly different depositional systems or, at the very least, to significant differences in the lateral position within the respective coastal sabkha depositional system.